1. Field of the Invention
This invention relates to an article security element for being fastened to an article to protect the article against theft. Such security elements are typically used by retail outlets, especially clothing stores, to protect the clothing from being stolen. More particularly, the present invention relates to security elements which have at least one soft magnetic metal strip that is capable of being detected in a high-frequency electromagnetic field that is disposed, for example in a an exit doorway of a retail establishment.
2. Background Information
Article security elements of the type noted above are disclosed in particular in European Patent No. 0 123 557, which corresponds to U.S. Pat. No. 4,581,524. This publication discloses a security tag having several layers, in which a strip of soft magnetic metal is glued on a strip-shaped base layer. A cover layer, also in the form of a strip, is glued over the base layer and the strip of soft magnetic material. In this manner, an oblong security tag is constructed which is fastened to articles, e.g. textiles, which are to be protected against theft.
For detection of such a device, a security gate or door having both a transmitter coil to emit a high-frequency electromagnetic scanning field, and a receiver coil for measuring a response field emitted by the security label as a reaction to the scanning field can be positioned at the exit of the store. Then, if an attempt is made to carry an article protected in this manner through the exit, a theft alarm can be activated.
The strength of the response field emitted by the security tag is a function of the orientation of the security tag in relation to the scanning field. If the strip of soft magnetic material has the same orientation as the scanning field, so that the magnetic axis of the strip lies parallel to the direction of the scanning field, the entire strip can be remagnetized at the frequency of the scanning field, and the strip can therefore emit an electromagnetic response field, which can be detected by a magnetic field sensor designed as a receiver coil. If the strip, and thus also its "easy" axis of magnetization, are at a right angle to the scanning field, this scanning field cannot remagnetize the strip, and the strip essentially will not emit any detectable response field, and the stolen article might not be detected by the receiver coil.